RUI: Theoretical Study of Quantum Control and Coherence Preserving Strategies in Solid State Spin Qubits

Santa Clara University, Santa Clara CA

Investigators

Abstract

TECHNICAL SUMMARY This award supports theoretical research and undergraduate education focused on the design and modeling of quantum bits, qubits, realized by spins localized in semiconductor quantum dots. The study will elucidate several of the key aspects of spin-based quantum information processors, focusing on the physical mechanisms that govern the coherence properties of spins in quantum dots and enable their control and manipulation. Utilizing a variety of analytical and numerical techniques, the PI and his research students will study the fluctuating charge and nuclear environments, which play a crucial role in electron spin decoherence in exchange-coupled III-V quantum dots. Coherence properties of electron-spin qubits will be analyzed under various manipulation protocols, in the context of ongoing experiments and proposed qubit designs. New formulations that extend the validity of current theories of electron-spin dephasing will be explored. In addition, hybrid qubit designs that offer better decoherence immunity, such as three-spin qubits will be investigated along with coupling strategies for multi-qubit devices. Going beyond the currently employed decoupling pulse sequences, the PI will explore time-dependent control fields that can extend the evolution of the quantum mechanical spin states. Finally the work supported with this award will develop and model optical and electrical control methods that utilize the hyperfine interaction to generate entangled nuclear states, offering new level of control over the nuclear collective states. The program supported through this award will be carried out at Santa Clara University, a Primarily Undergraduate Institution, and will provide educational opportunities for undergraduate students through independent research projects throughout its duration. Students will take active part in cutting-edge physics research that will train them in advanced theoretical methods and high-end numerical analysis. The research will employ a variety of methods and work modalities, ranging from many-body problems and spin physics in semiconductor heterostructures to code writing for parallel computing computer cluster environment. This diversity ensures that students can pursue multiple and independent lines of investigation so that self-contained research projects will be completed within a full-time summer period. Participating students will be exposed to the leading experimental and theoretical endeavors in the highly vibrant and interdisciplinary research field of quantum computing. NON-TECHNICAL SUMMARY The wide-spread interest in quantum information processing in recent years has been a critical driving force in the research of electron spins localized in semiconductor quantum dots. The spins are associated with electrons; spin is an intrinsic quantum mechanical property that can be exploited to make a two-state quantum mechanical system, or qubit, in the engineered mound of a semiconductor surface or quantum dot. This award supports a theoretical research and undergraduate education program aimed at elucidating several of the key aspects of spin-based quantum information processors, focusing on the physical mechanisms that govern the coherence properties of spins in quantum dots and enable their control and manipulation. The two main ingredients of a successful design of qubits - the building blocks of a quantum computer - are preserving the coherence of their fragile states and finding mechanisms that will allow high fidelity qubit control and manipulation at the single- and two-qubit level. Addressing the first, the PI and his research students will model and analyze the fluctuating charge and nuclear environments, which form the main decoherence channels for electron spin qubits. A better understanding of the adverse effects of the environment on spin qubits at current experimental setups will allow the team to test and propose strategies to extend coherence, including time-dependent control fields, novel qubit designs, and encoding of the logical states in physical states of three electron spins. The research supported by this award will further explore coupling strategies for multi-qubit devices and develop optical and electrical methods to control the nuclear spins in the quantum dot substrate, by utilizing their hyperfine interaction with the localized electron spins. The program supported through this award will be carried out at Santa Clara University, a Primarily Undergraduate Institution, and will provide educational opportunities for undergraduate students through independent research projects throughout its duration. Students will participate in cutting-edge physics research that will train them in advanced theoretical methods and high-end numerical analysis. A variety of theoretical methods and work modalities will ensure that students will pursue multiple and independent lines of investigation so that self-contained research projects can be completed within a full-time summer period. Participating students will be exposed to the leading experimental and theoretical endeavors in the highly vibrant and interdisciplinary research field of quantum computing.